1. Field of the Invention
The present invention relates to a polymerizable composition that can yield an unreleasable antimicrobial polymer and, more specifically, to a polymerizable composition capable of yielding an unreleasable antimicrobial polymer from which the antimicrobial component is not released, and the polymer and medical articles obtained from the composition.
The medical articles produced according to the present invention includes artificial blood vessels, artificial skin, wound-covering materials, catheters, sutures, dental materials (adhesives, coating agents, composite resins and the like), contact lens, bone cement and the like.
2. Description of the Prior Art
Polymers having antimicrobial properties are known. For example, polymers containing a releasable antimicrobial component have this property. It has been considered necessary that an antimicrobial component be entrapped by bacteria or enclosed by then to be effective and kill or inactivate them. For this purpose, it has been considered necessary that the antimicrobial component elute, i.e. be released, from the polymer to contact the bacteria without restriction. For example, "Synthesis and Antibacterial Activities of Copolymers Having a Quaternary Salt Group", on pages 934-939 of METAL, INORGANIC AND POLYMER MATERIALS, the 9th series, which discloses research and development issued from the Agency of Industrial Science and Technology, reports that an acrylonitrile copolymer containing ammonium chloride groups is released to develop an antimicrobial property against Bacillus subtilis or Staphylococcus aureus. Japanese Patent Application Laid-open No. 201806/1987 discloses an antimicrobial dental composition containing cetylpyridinium chloride that is a known cationic surfactant.
By releasing the anitimicrobial component, however, the antimicrobial activity decreases over time and is lost when the active component is gone. Antimicrobial components often give hazardous action to normal tissue and after, having been released, they migrate also to normal tissue, whereby it is impossible to prevent the hazardous action completely. Incorporation of antimicrobial agents often causes the matrix to decrease its mechanical properties.
The antimicrobial activity in the field of dental materials is briefly described below. Caries, which is a representative dental disease, develops by dissolution of enamel with acids produced by bacteria in the oral cavity. Streptococcus mutans is an important bacterium causing caries. Periodontitis, which is a disease of periodontal tissue, also develops by bacteria present in the oral cavity. It is important for preventing either of these diseases to prevent the bacteria from forming plaque on the surface of dentin or to remove the plaque quickly once formed. Regular toothbrushing is recommended to these ends.
Where a dental prosthesis has been used to fill or restore a caries with a dental material such as a resin or composite resin, it is also important, for the purpose of preventing the development of secondary caries or periodontitis, to remove plaque that readily forms on the surface of the material caused by adhesion of bacteria.
To prevent caries, a known practice is the topical application of fluoride, i.e. application to dentin of an acid phosphoric fluoride (APF) solution or a diamine silver fluoride solution, which improves the acid resistance of enamel. Several attempts have also been made, while paying attention to the dental material used, to prevent plaque from depositing on, the material. Thus, incorporation of antimicrobial agents in dental materials has been attempted, and there have been reported, for example, a composite resin incorporating chlorohexidine (K. Takemura et al, The Japanese Journal of Conservative Dentistry, Vol. 26, (2), 540-547, 1983), calcium phosphate-based cement incorporating metronidazole (M. Iwaku et al, The Japanese Journal of Conservative Dentistry, Vol. 30, (5), 1444-1448, 1987).
Such simple incorporation of an antimicrobial agent in dental material, however, cannot assure satisfactorily durable antimicrobial activity, since the agent is entirely released in a short period of time. The incorporation further has the problem of decreasing the mechanical properties of the matrix material.
Furthermore, releasing of an antimicrobial agent contained in a dental composition may, while influencing the surface of the composition, badly influence bacterial flora surrounding the composition in the oral cavity.